1. Field of the Invention
This invention involves a process for high selectivity, short contact time, catalytic transalkylation of alkylaromatic hydrocarbon compounds of from 7 to 10 carbon atoms, e.g. toluene, wherein the transalkylation is performed in a fluidized catalyst system absent added hydrogen. The catalyst for use in the present process is a porous acid-active zeolite having a fluid activity index of at least about 18. High selectivity to desired product, e.g. greater than equilibrium amounts of paraxylene from a feedstock of toluene, is achieved by way of the present process when reaction conditions are maintained within the following approximate ranges:
______________________________________ Reactor inlet temperature 300 .degree. F - 1200.degree. F Reactor pressure 0 psig - 200 psig Catalyst/alkylaromatic hydrocarbon compound feedstock (wt/wt) 1 - 60 Catalyst residence time 0.01 second - 300 seconds Feedstock residence time 0.01 second - 300 seconds Slip ratio, defined as the ratio of catalyst residence time to feedstock residence time 1 - 2 ______________________________________
2. Description of Prior Art
U.S. Pat. No. 3,551,509discloses transalkylation between trimethylbenzenes and toluene to yield xylenes and benzene in the presence of a crystalline aluminosilicate catalyst having pore openings of 8 to 15 Angstrom units and, preferably containing Group VIII metals, hydrogen and rare earth cations. The above patent is also the subject of U.S. Pat. No. Re. 27,639.
In the area of aromatic disproportionation, Grandio et al. teach in the Oil and Gas Journal, Vol. 69, Number 48 (1971) a liquid-phase toluene disproportionation process utilizing zeolite catalysts in the absence of hydrogen. They further teach that vapor-phase toluene disproportionation requires hydrogen recycle or else frequent regeneration of catalyst to keep coke levels low on the catalyst and to maintain catalytic activity over any reasonable period of time.
Otani teaches in Chemical Engineering, 77(16), 118 (1970), that vapor-phase catalytic disproportionation of toluene requires hydrogen recycle to keep the zeolite catalyst from excessive coke build-up and, thereby, maintain reasonable catalyst activity.
U.S. Pat. Nos. 3,126,422; 3,413,374; 3,598,878; 3,598,879; and 3,607,961 show vapor-phase disproportionation of toluene over various catalysts.
Unfortunately, while many of the prior art processes proposed for transalkylation, including disporportionation, of alkylaromatic hydrocarbon compounds provide satisfactory initial yields of desired products, they do not provide the short contact time, high selectivity benefits associated with the present process. Further, no hydrogen is used in the present process, the presence of which is taught to be necessary by the prior art, thus enabling the user of the present process to realize substantial processing economies.